Alignment of a prosthesis is an important element of optimizing its function. FIG. 1 illustrates a representative prosthesis for a transtibial amputee. The prosthesis 10 includes a foot portion 20 rigidly, but adjustably, affixed to a pylon 30. The pylon 30, in turn, is connected to the prosthesis socket 60 via a tube clamp adaptor 40 and a pyramid adaptor 50. The connection between the tube clamp adaptor 40 and the prosthesis socket 60 is adjustable to fix the alignment. Although not shown, the tube clamp adaptor 40 has an concave spherical, load-bearing surface on the upper end of the tube clamp adaptor 40. This surface includes a central hole through which the tube clamp adaptor 40 receives the pyramid adaptor 50. The pyramid adaptor 50 is so named because of the inverted pyramid-shaped protuberance that fits into the central hole of the surface in the tube clamp adaptor 40. The pyramid adaptor 50 has a convex spherical load-bearing surface designed to be supported by the concave spherical surface on the tube clamp adaptor 40 that allows articulation in directions relative to the horizontal plane. In terms familiar to aviation, these are “pitch” and “roll.” Thus, the pyramid adaptor 50 can be oriented in any configuration in the anterior/posterior plane, as well as the right/left plane. The pyramid adaptor 50 is locked in place by tightening four set screws (not shown) that press against the respective four sides of the inverted pyramid. The pyramid adaptor 50 further has an upper flange that rigidly attaches to the underside of the prosthesis socket 60. In a prosthesis, the alignment of the socket 60 and pylon 30 affects the functional performance and comfort of the person by altering the manner in which the weight-bearing load is transferred between the amputated limb and the ground.
The importance of alignment has been recognized for many decades, but little progress has been made to give a prosthetist the tools needed to optimize this aspect of prosthetic care. Until now, prosthesis alignment has been an imprecise and inconsistent practice based primarily on the subjective opinion and the experience of the prosthetist to visually determine the proper alignment.